Preface

Lean production has revolutionized manufacturing over the last several decades. Frameworks like TQM, Just-In-Time, Theory of Constraints, and the Toyota Production System have vastly improved the general state of automotive and manufacturing quality and spawned a vital competitive landscape. The family of Agile software development approaches brings the principles of Lean production to the knowledge discipline of software product development, but it needs to adapt these principles to a less mechanical context.

The idea of building the quality into the product in order to increase customer satisfaction and reduce the overall lifetime cost of maintenance has resulted in practices like test-driven development (TDD) and other test-first and test-early approaches. Regardless of which flavor you espouse, you need to understand what testable software looks like and master a wide range of techniques for implementing tests to be successful. I have found the gap between the principles and the state of the practice is often an unacknowledged source of failure in testing regimens. It is easy to say “use test-driven development,” but when faced with a project, many developers do not know where to start.

In showing people how to apply test-driven, or at least test-early, development, I often find that one of the obstacles is the mechanics of writing tests. Exercising a method as a mathematical function that purely translates inputs to easily accessible outputs is no problem. But much software has side effects, behavioral characteristics, or contextual constraints that are not as easy to test.

This book arose from a recurring need to show developers how to test the specific situations that stymied them. Consistently, we would sit down for a few minutes, we would write a unit test for the troublesome code, and the developer would have a new tool in his belt.